X-rays and other radiographic analysis are important diagnostic tools. In order to rely on data extracted from radiographs, it is often helpful to include a phantom of known radiopacity. Calibration references (also known as calibration phantoms) for use in imaging technologies have also described. See, e.g., U.S. Pat. No. 5,493,601 and U.S. Pat. No. 5,235,628. U.S. Pat. No. 5,335,260 discloses a calibration phantom representative of human tissue containing variable concentrations of calcium that serves as reference for quantifying calcium, bone mass and bone mineral density in radiography and CT imaging systems. However, currently-available calibration phantoms are not always accurate, due to both the effect of structures or materials that project on or with the calibration phantom and, additionally, to the fact that one or more regions of the calibration phantom do not always appear on the x-ray image.
Thus, there remains a need for calibration devices that provide references for density and geometry of the images structures.